Noncoherent receivers for differential space-time modulation

An architecture of decision feedback differential phase detection (DF-DPD) of M-ary DPSK signals is proposed. Conventional differential detection of M-ary DPSK signals uses the phase difference between a current symbol and the previous symbol. This method can make the receiver architecture simple. But it has poorer BER performance than coherent detection because it uses the previous noisy signal as the phase reference. To improve the BER performance of conventional differential detection, multiple symbol differential detection methods, such as maximum likelihood differential detection (ML-DD), Viterbi-DD, decision feedback differential detection (DF-DD), and DF-DPD, using L-1 past detected symbols, have been proposed. As L increases, the BER performance of DF-DPD improves but the complexity of the architecture increases dramatically. Thus, this paper proposes the simplified DF-DPD architecture, replacing the conventional delay and addition architecture with one accumulator. The proposed architecture also has a good BER performance with minimizing the phase error of the current received symbol using the accumulated phase differences of all DPD. The simulation results show that the BER performance of the proposed architecture approaches that of coherent detection.

In cognitive radio networks, power control is considered to be a very important concern where secondary users, which are equipped with cognitive radios, try to access the unused spectrum of licensed primary users in an opportunistic way. Cognitive radios enable the secondary users to sense the presence of primary users and tune the channel (spectrum band) which is not in use at any time for its use. However, the interactions between secondary users are the only parameters which have been considered in most of the existing studies in this space, and the impact of primary user behaviors has been ignored. Hence, a novel realistic primary-secondary game-theoretic scheme is proposed in this study which rewards primary user for sharing its spectrum and allows secondary users to achieve energy-efficient transmissions. In general, the additive white Gaussian noise channel model is considered to be poor to describe the transmission channel and one must resort to more precise and realistic models such as fading channels. The proposed work here extends the fast flat fading models investigated in [1] and [2] to consider slow flat fading channels, where Rayleigh slow flat fading channel is analyzed and a closed-form expression is derived for the average utility functions. The existence and uniqueness of Nash equilibrium are also shown. Finally, detailed simulation results are presented to verify the performance of the scheme under realistic channel conditions compared to AWGN channel model.

Recently we proposed a novel differential encoder by a look-up table. In this paper, we present further research results on this subject. We first propose a bit-assigning algorithm and construct some new tables for various constellations that maximize the minimum noncoherent distance. Then differential encoding for multiple-symbol differential detection is proposed. After that, we indicate that differential encoding by a table is equivalent to differential encoding by a trellis, so we propose a novel differential detector which uses the Viterbi algorithm on the trellis. A theorem about the sufficient number of states for various modulations is proposed. In addition, we further enhance the error performance of the proposed differential encoder by concatenating it with trellis coding. For this noncoherent trellis coding scheme, we propose augmented-state Viterbi decoding. Finally, we extend the proposed differential encoding and detection to differential space-time modulation (DSTM). We propose a new definition of DSTM by which the set of transmitted blocks is determined first. The differential encoding is implemented by a look-up table which can be optimized. The proposed DSTM has satisfactory error performance without constellation expansion.

Multiple-symbol differential detection (MSDD) is a robust maximum-likelihood (ML) receiver technique for frequency-nonselective fast Rayleigh fading channels. However, its complexity grows exponentially with the block size N and that makes it impractical to implement. Recently, multiple-symbol differential sphere decoder (MSDSD) is developed to alleviate this problem but its complexity at low signal-to-noise ratio (SNR) grows exponentially with decreasing SNR. In this paper, we explore the potential of the Fano algorithm as an efficient MSDD receiver. The bit-error performance and the complexity of the Fano-MSDD are evaluated and compared with other reduced complexity techniques. Our preliminary results indicate that Fano-MSDD is more attractive than decision-feedback differential detection (P.Y. Kam and CH Teh, 1983) and (R Schober and WH Gerstacker, 2000) from both the error performance and the complexity points of view. When compared to the MSDSD, the Fano-MSDD suffers a moderate degradation in power efficiency. However, its computational complexity is very steady even at low SNR. This translates into a dramatic saving in complexity over the MSDSD when SNR is low. Even at large SNR, the Fano-MSDD still provides a small edge over the MSDSD in terms of complexity. We believe that with some fine tuning of the decoder parameters, such as the bias and the threshold's step size, it is possible to extract better performance from the Fano decoder than it is now.

The performance of multiple symbol differential detection applied to differentially encoded QPSK signals, is examined by simulation in the mobile radio channel with slow Rayleigh and Rician fading, and cochannel interference (CCI). Performance gains observed in the slow Rician fading channel when compared to conventional differential detection, are maintained in the CCI environment. Using a signal quality measure from the multiple symbol differential detection algorithm for selection diversity, performance gains are observed over conventional differential detection in Rayleigh fading as well. >

Our goal in this paper is to study the performance of the game-theoretic power control algorithms for wireless data introduced by Saraydar et al [1] in two realistic channels: (a1) fast flat fading channel and (a2) Slow flat fading channel. The fading coefficients under both (a1) and (a2) are studied under an appropriate small scale channel model that is used in the CDMA cellular systems, namely Nakagami channel model. To do so, we derive a closed- form expression of the average utility function which represents the number of bits received correctly at the receiver per one Joule expended. Then, using this expression we study the existence, uniqueness of Nash equilibrium (NE), and the social desirability of NE in the Pareto sense.

In this study, the authors study the modulation classification of linearly modulated signals including amplitude shift keying (ASK), phase shift keying (PSK) and quadrature amplitude modulation (QAM) signals. The authors consider an unknown frequency non-selective slowly fading channel with an unknown variance additive white Gaussian noise. The authors treat this classification problem as a multi-hypotheses test which is invariant under the complex scale. In such a case, the authors objective is to find uniformly most powerful (UMP) test in the class of invariant decisions. However, the authors find out that the UMPI test does not exist; instead, they provide a most powerful invariant (MPI) PSK signal classifier for known signal to noise ratio and use it as the upper performance bound for any invariant classifier. The authros also propose a hybrid likelihood ratio test (HLRT) solution which can be employed for the classification of linearly modulated signals, inter-family and intra-family. The authors also explain the efficient implementation of these algorithms in some steps. In order to reduce the computational cost, the authors propose quasi-HLRT classifiers for PSK signals. Some simulation examples are provided that show the power of the proposed algorithms in the classification of linearly modulated signals.

Existing work on decision feedback detection (DFD) of differential space-time modulation (DTSM) were largely confined to diagonal constellations. In other works considering nondiagonal constellations, the temporal variation of fading in the DTSM supersymbol duration was ignored. In this paper, we take a close look at the DFD receiver structure for nondiagonal DSTM in temporally correlated fading. We identify the constellations of which the error performance is not influenced by ignorance of fading variation. In addition, by analyzing the error performance, we demonstrate that existing DFD, is however, fundamentally mismatched to other constellations in fast fading. A major conclusion is that diagonal design still plays an important role for the efficacy of DFD for nondiagonal constellation in fast fading.

기존 Zhu가 제안한 준직교 기반의 차등시공간변조(Differential Space-Time Modulation, DSTM)는 복소 선부호기와 준직교 시공간블럭부호를 연접하여 차등변조기법으로 전송함으로써 수신단에서 채널 정보 추정 없이 2개의 복소 신호들에 대한 독립적인 복조, 즉 준직교 차등복조가 가능하다는 장점을 갖는다. 본 논문에서는 이와 같은 준직교 기반 Zhu-DSTM를 기반으로 복소 선부호기 대신 실수 선부호기를 사용함으로써 수신단에서 2개의 실수 신호들에 대한 독립적인 차등복조가 가능하게 하여 수신 복잡도를 더욱 줄일 수 있는 새로운 DSTM를 제안한다. 전산 실험 결과 제안된 기법은 기존의 준직교 기반 DSTM들과 거의 같거나 향상된 성능을 가짐을 확인할 수 있으며 따라서 수신 복잡도 및 수신 성능 측면에서 큰 장점을 가지게 된다. The conventional Zhu's differential space-time modulation(DSTM) based on quasi-orthogonal design adopted a complex precoder in order to allow an independent joint detection of two complex symbols without any channel informations at a receiver. In this paper, by simply replacing the complex precoder used in Zhu's DSTM with a real precoder, a new DSTM is presented for four transmit antennas. The real precoder enables the receiver to decode two real symbols pair separately, and thus the new DSTM has greatly reduced decoding complexity compared to the Zhu's DSTM. By computer simulation results, the proposed scheme is shown to exhibit almost identical or improved error performance compared to the existing DSTMs.

A conventional decision feedback differential detection technique can be regarded as a technique using L previously received signal samples and L-1 previously decided data phases to generate a phase reference for the phase detection operation of a currently received MPSK signal sample. With this observation, we propose a differential detection technique which uses a new way to generate the phase reference. In the proposed technique, the phase reference called weighted phase reference is the weighted sum of primitive phase references derived from previously received signal samples. The weighted phase reference can be generated using a simple recursive form. The proposed detection technique can be easily implemented and has satisfactory error performance.

In this paper we present decision-feedback differential detection (DF-DD) schemes for autocorrelation-based detection in impulse-radio ultra-wideband (IR-UWB) systems, a signaling scheme regarded as a promising candidate in particular for low-complexity wireless sensor networks. To this end, we first discuss ideal noncoherent sequence estimation and approximations thereof based on block-wise multiple-symbol differential detection (MSDD) and the Viterbi algorithm (VA) from the perspective of tree-search/trellis decoding. Exploiting relations well-known from tree-search decoding, we are able to derive the novel decision-feedback differential detection (DF-DD) schemes. A comprehensive comparison with respect to performance and complexity of the presented schemes in a typical IR-UWB scenario reveals-along with novel insights in techniques for complexity reduction of the sphere decoder applied for MSDD- that sorted DF-DD achieves close-to-optimum performance at very low, and in particular constant receiver complexity.

In this paper, differential modulation diversity (DMD) is introduced. This diversity scheme is based on diagonal signal constellations which have been previously proposed for differential space-time modulation (DSTM). DMD can exploit both space and time diversity and DSTM, which is a pure space diversity scheme, results as a special case. A low-complexity noncoherent receiver originally designed for DSTM is adapted to DMD and the power efficiency of DMD for spatially correlated Rayleigh fading and imperfect interleaving is investigated.

Simple closed-form solutions for the average error rate of several coherent modulation schemes including square M-QAM, DBPSK and QPSK operating over slow flat Rician fading channel are derived. Starting from a novel unified expression of conditional error probability the error rates are analysed using PDF based approach. The derived end expressions composed of infinite series summations of Gauss hypergeometric function are accurate, free from any numerical integration and general enough, as it encompasses as special situations, some cases of non-diversity and Rayleigh fading. Error probabilities are graphically displayed for the modulation schemes for different values of the Rician parameter K. In addition, to examine the dependence of error rate performance of M-QAM on the constellation size, numerical results are plotted for various values of M. The generality of the analytical results presented offers valuable insight into the performance evaluation over a fading channel in a unified manner.

In conventional differential detection (CDD), the previous received symbol is used as the phase reference for the current received symbol, therefore the channel variation due to fast fading causes an error floor. We propose a novel iterative decision-directed differential detection (iD4) algorithm for orthogonal frequency division multiplexing (OFDM) systems employing differential PSK modulation in each subcarrier. The core of iD4 is a low complexity time and frequency 2-D estimator which can effectively estimate the channel variation experienced by adjacent time domain symbols. This estimated channel variation is then compensated in the differential detection process. Both theoretical analysis and computer simulations show that significant performance improvement can be achieved using iD4 over the CDD for OFDM receivers in fast fading channels.

Estimation of the signal-to-noise ratio (SNR) is considered for a non-coherent M-ary frequency shift keying (NC-MFSK) receiver. It has been assumed that the transmitted symbols undergo a slow flat fading channel where a block of data is corrupted by an independent constant fade and additive white Gaussian noise. Two approaches for SNR estimation are reported in this paper: an approximate maximum likelihood approach and another using the data statistics, both for data aided and non-data aided systems. It has been shown that for a particular SNR region of interest and depending upon the availability of pilot symbols, a particular approach is suitable for SNR estimation.